Radiant burner for gaseous fuel

ABSTRACT

In a radiant burner whose head has a ceramic incandescent body with individual burner channels, the interior of the incandescent body (3) is provided with a metallic coating (7) which extends into each of the burner channels (6) and which is closed except at the entries to the channels.

BACKGROUND OF THE INVENTION

The invention pertains to a radiant burner as described in the preambleof claim 1 and to a process for producing a burner head and anincandescent mantle for such a radiant burner.

PRIOR ART

Radiant burners with ceramic burner heads have been known for a verylong time. The susceptibility of the ceramic body to cracking is aserious problem in burners of this type. This has an unfavorable effecton the life of the burner and necessitates expensive and time-consumingrepair and installation work. The lost operating time of a system thatuses these burners is another important consideration. Even small cracksin the incandescent mantle can lead to significant problems in theoperation of the burner, because they are undesired passages for theoperating medium, which can cause back-ignition and other problems.

BRIEF DESCRIPTION OF THE INVENTION

The goal of the invention is to eliminate as far as possible thepreviously observed problems and disadvantages and to create a radiantburner with a burner head made of ceramic or comparable material. Thisburner must have favorable characteristics, including especiallyresistance to cracks in the ceramic body, to eliminate the problems ofback-ignition and short service life. The invention also intends toprovide a more favorable design for a radiant burner. The invention alsodeals with other, related problems that are described in detail below.

In a radiant burner of this type, the invention proposes that theincandescent body be provided with a metal lining on its inside or rearside, i.e., the side facing the housing. The metal lining extendspartially into the burner channels in regions called intake sections andis sealed except for the burner channel intakes formed in this way.

This means that the rear side of the incandescent body has animpenetrable seal that extends into the burner channels. Even if cracksor fractures develop in the incandescent body in the course of time,they cannot have a harmful effect on the operating behavior of theburner, because the path for any fuel-air mixture entering such cracksis blocked by the lining to the rear, including the intake regions tothe channels. The problems that can arise in conventional burners due tocracks and the like in the incandescent body are rendered harmless here.Therefore, even if cracks should develop, the burner can continueoperating, which means that expensive repairs are avoided, and theservice life of the burner is increased. The prevention of back-ignitionthat is achieved does not depend on the particular load on the burner.In other words, it is also possible to operate the burner at greatlyreduced capacity, as is often desired, at least temporarily.

The lining can be made of a variety of metals, depending on the intendedpurpose of the burner and the requirements that it must satisfy.Examples of suitable metals are iron and especially heat-resistantsteel.

In many cases it is sufficient for the intake sections of the lining tosurround only the edge areas at the ends of the channels. In othercases, it may be advantageous for the intake regions to extend fartherinto the burner channels, especially about halfway along the length ofthe channels or even farther.

In one effective design, the intake sections and the rest of the liningconsist of a single piece. This type of piece can be produced especiallyby the shaping (e.g., pressing, punching, piercing, or a combination ofsuch operations) of a platelike workpiece provided as the lining,especially a piece of sheet metal.

It is also possible, however, to produce the intake sections as partsthat are separate from the flat lining and to join them to the liningduring the construction of the burner head. The two parts can be joinedpermanently or detachably, either by a positive interlocking connectionof the parts or by a friction-locking connection, e.g., a force fit.

The lining can rest directly against the incandescent body. Depending onthe requirements, however, it is also possible to provide anintermediate layer between the incandescent body and the metal lining,especially a layer consisting of heat-resistant nonwoven fabric or alayer of a refractory compound.

This is advantageous especially when a prefabricated incandescent bodyconsisting of one or more parts, e.g., a ceramic plate, is to be joinedto the lining to form the burner head. The purpose of the intermediatelayer may merely be to even out any small dimensional variations thatmay be present in the parts. It can also be used as a special joiningmaterial and may be composed to produce reliable adhesion between theparts.

The burner channels, at least in the parts next to the outer side of theincandescent body, can have a rotationally symmetric cross section withflaring, especially with a more or less curved contour.

In another advantageous design of the invention, the burner channelshave a basically star-shaped cross section, at least in a part next tothe outside of the incandescent body. The cross section has a centralregion and radial spaces which radiate from the central region and whichare open towards the outside of the incandescent body. The centralregion can be open, or it can be closed towards the outside. Anadvantageous number of radial spaces is two to six, but the number canalso be larger.

In another advantageous design, the burner channels can continue into atleast two obliquely running individual channels, at least in a part nextto the outside of the incandescent body. Here again, the number ofchannels is advantageously two to six, but a larger number is possible.

The various designs discussed above allow especially reliable operationof the radiant burner, achievement of a high degree of efficiency,operation at high temperatures, and rapid and intense heating of theincandescent body. These designs are especially important.

Another advantageous feature is that, regardless of the rest of theradiant burner's design, the burner channels or their parts end inoutside recesses in the incandescent body. These recesses can bedesigned in various ways. It is especially advantageous to design themas areas enclosed by riblike projections of the incandescent body.Designs of this type have the advantage that the outlets of the burnerchannels are located in a protected area, so that negative effects ofair currents on the front side of the burner are prevented or at leastgreatly reduced.

In one design of the burner, a space is provided on the side of thelining that faces away from the incandescent body. The fuel-air mixtureis fed into this space and then flows into the burner channels.

In another advantageous design, a space is provided on the side of thelining facing away from the incandescent body for receiving at least onecomponent of the fuel-air mixture. Supply lines for at least one othercomponent of the fuel-air mixture, which are closed off from this space,are assigned to the burner channels, which open into the space. It isadvantageous for these supply lines to extend into the burner channels.

The medium flowing through the supply lines picks up the medium in theneighboring space, so that a jet or injector effect is obtained, andintensive mixing and good flow conditions are achieved. It is especiallyadvantageous to supply gas through the supply lines while air flows fromthe neighboring space, but an opposite arrangement is also possible.

In a radiant burner of this type, in which supply lines for one mediumare assigned to the individual burner channels of a burner head, it ishighly desirable for the burner channels to have either a round crosssection (especially a circular cross section), at least in that partinto which the supply lines extend, or an oval cross section, and alsofor the supply lines to have a polygonal cross section, at least intheir terminal sections, which extend into the burner channels. Anopposite design is also possible, however. Specific cross-sectionalratios can be achieved in this way.

In these types of designs, it is desirable to support at least the endsof the supply lines in the burner channels. Together with additionalmounting of the supply lines, this provides for good centering.

As mentioned earlier, the incandescent body of the burner head can beproduced separately from the lining, and then the two parts can bejoined. It is also possible in accordance with the invention to apply asuitable compound for the formation of the incandescent body to aprefabricated lining. The compound is then hardened by drying, curing,baking, or some other process. The burner channels can be molded withtemplates, molds, or the like, or they can be produced later if they arenot already formed by the inlet sections of the lining. A simplebox-like mold, such as a sheet metal box, can be used to apply thecompound for the incandescent body. It is also possible to use partssimilar to a concrete form, to enclose and hold the compound as it isapplied or poured. Depending on its nature and consistency, the compoundcan be applied by casting or pouring and especially by tamping orspraying.

Compounds that can be used for the incandescent body includecompositions containing aluminum oxide, silicon dioxide, zirconiumoxide, or similar substances. Materials are available which areextremely well suited to the production of an incandescent body with ametal lining. Modern materials, such as those used to produce or restorelinings in industrial furnaces, especially ceramic fiber materials, areespecially attractive for the production of incandescent bodies. Highlyrefractory materials are also available, and burners containingincandescent bodies made from these materials can be operated at hightemperatures.

Further details, features, and advantages of the invention can bederived from the following specific examples, from the attacheddrawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first design of a radiant burner, partially cutaway.

FIG. 2 is a cutaway of part of the lined incandescent body on a largerscale.

FIG. 3 is a top view of FIG. 2.

FIG. 4 is a modified design of a section corresponding approximately tothe section shown in FIG. 2.

FIG. 5 shows additional detail in a cutaway view.

FIG. 6 is another partially cutaway design of a radiant burner.

FIG. 7 is a cutaway section of the incandescent body of the burner inFIG. 6 on a larger scale.

FIG. 8 is a cross section along line VIII--VIII in FIG. 7.

FIGS. 9-11 show modified designs in approximately the same crosssections as FIG. 8.

FIG. 12 is another design of a burner channel and shows a top view ofthe outside of the incandescent body.

FIG. 13 is a cross section along line XIII--XIII in FIG. 12.

FIG. 14 is another design of a burner channel in a top viewcorresponding to FIG. 12.

FIG. 15 is a cross section along line XV--XV in FIG. 14.

FIG. 16 is a partial top view of the outside of an incandescent bodythat is specially designed in this section.

FIG. 17 is a cross section along line XVII--XVII in FIG. 16.

FIG. 18 is a partial top view of the outside of a specially designedincandescent body.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The infrared radiant burner shown in FIGS. 1-3 has a sheet metal housing1 that encloses a space 2. A supply line 5 for a mixture of fuel gas(which may be gaseous or vaporized fuel) and air opens into this space.This mixture is produced by means that are already known for burners ofthis type and is supplied to the burner via suitable fittings, so thatthere is no need to discuss this subject in detail here.

The forward area of the burner (shown at the bottom in the drawing) hasan incandescent body 3 made of a heat-resistant material. Incandescentbody 3 is positioned in a shoulder 1a of housing 1 and is held in placeby flanges, for example, at different points along the edge of thehousing and/or with a refractory material 4 that fills the gap aroundthe burner between the incandescent body and the housing. This alsoserves to seal the burner in these areas. Incandescent body 3, whichhas, for example, a basically square or rectangular shape, is providedwith a number of burner channels 6, which are distributed regularly orin some particular pattern over the surface of the incandescent body.Burner channels 6 widen towards the outside, as is apparent in FIGS. 1and 2. The wall can be straight, but it is more advantageous to havecurved walls, as shown in the drawings. The shape and length of thewidening of the burner channels depends on the requirements of eachindividual case. The shape and length of the widening are selected insuch a way that the stream of gas mixture decelerates until at a certainpoint in the channel the conditions with respect to the rate of flamepropagation are such that combustion stops at that point.

The inner side of incandescent body 3 is provided with a basicallyplatelike lining 7, which in this design is made of refined steel plateand is fitted tightly to the incandescent body. Together with inletsections 8, which are formed from the plate itself, lining 7 extendsinto burner channels 6, so that it also covers the incandescent body inthese areas. The inlets of channels 6 have a larger diameter on the sidecoming from mixing chamber 2 than at the narrowest channel crosssection, and the diameter decreases towards that narrowest point.

The length of inlet sections 8 can vary, depending on the circumstances.It is advantageously about half the total length L of channels 6, but itcan also be smaller or larger.

Lining 7 completely seals incandescent body 3 towards the inside, i.e.,on the side facing chamber 2, so that even if cracks should develop inthe incandescent body, no back-ignition can occur through these cracks.

Lining 7 can be flat at its edges. It can surround the edges ofincandescent body 3 or have, for example, high bent edges 7a, which fittightly against shoulder 1a of housing 1.

In the design shown in FIGS. 1-3, inlet sections 8 and lining 7 consistof one piece. FIG. 4 shows a design in which inlet sections 8' areseparately produced parts that are inserted in holes in lining 7' andrest on lining 7' with a flangelike edge 8a. Parts 8' can be firmlyattached to plate 7' by pressing them into holes 9, or they can bemounted on the plate by other suitable means.

In the designs shown in FIGS. 1-4, the material of incandescent body 3rests directly against the underside of lining 7. FIG. 5 shows a designin which an intermediate layer 10 is located between incandescent body 3and lining 7. This layer can consist in particular of a nonwoven fabric.

FIGS. 6-8 show another design of a radiant burner. A metal housing 11contains two chambers 12 and 13, which are separated from each other bya wall 14. A supply line 15 for fuel gas opens into chamber 12, while asupply line 16 for combustion air opens into chamber 13. Supply lines 17in the form of metal tubes are mounted firmly and tightly (e.g., bywelding or soldering) in holes in partition wall 14.

As in the design discussed above, the burner has a burner head with anincandescent body 3 containing burner channels 6 and is covered by alining 7, 8. Parts that are the same as parts in FIGS. 1-3 or thatcorrespond to those parts are labeled with the same reference numbers asin FIGS. 1-3. Everything said about these parts in connection with FIGS.1-3 also applies here.

Each burner channel 6 has a supply line 17, which extends a certaindistance into burner channel 6. The ends of supply lines 17 do not needto be in contact with the wall of the burner channel. In this case,supply lines 17 are supported only by partition wall 14. It is notcritical for the axes of supply lines 17 be exactly coaxial to thelongitudinal axes of associated channels 6. The medium flowing fromchamber 12 through supply lines 17 draws the medium in chamber 13 withit, so that intensive mixing takes place, and the resulting combustiblemixture continues to flow in the channel until it burns at the desiredpoint in the channel.

Chamber 12 was specified above as the intake chamber for fuel gas, andchamber 13 was specified as the intake chamber for combustion air.However, the opposite may also be the case; i.e., chamber 12 may besupplied with air through supply tube 15, while chamber 13 is suppliedwith fuel gas through supply tube 16.

FIG. 8 shows a supply line 17 with a circular cross section and a burnerchannel 6, which also has a circular cross section. Other designs arealso possible, such as those shown in FIGS. 9-11, which showapproximately the same cross section as in FIG. 8. In these designs, thedimensions of the supply lines and burner channels can be selected insuch a way that the ends of the supply lines are supported by the wallsof the burner channels or by the inlet sections of the lining.

FIG. 9 shows a supply line 19 in the form of a tube with a square crosssection, and FIG. 10 shows a supply line 20 in the form of a tube with atriangular cross section. In each case, burner channel 6 has a circularcross section. In the design shown in FIG. 11, burner channel 6' andthus inlet section 18 of the lining have a square cross section, whilesupply line 17 has a circular cross section.

Depending on the circumstances and requirements and regardless of thespecific design, the burner can also be equipped with a grate, screen,or the like, which is placed in front of the incandescent body. In FIGS.1 and 6, such a screen is indicated in broken lines and labeled with thenumber 30.

FIGS. 12 and 13 show another design for a burner channel 26. Following acylindrical part 25, the burner channel has an essentially star-shapedcross section with a central region 27 and more-or-less groove-likeradial spaces 28, which extend outward from central region 27 and whichare open towards the outside of incandescent body 23. These radialspaces 28 have boundary surfaces 29, which run obliquely to the axis ofburner channel 26 and form the base of the groove; they have arectangular cross section, as the drawings show. However, a differentcross-sectional shape can be chosen.

Central region 27 can be open or closed towards the outside ofincandescent body 23. The latter case is shown in FIG. 13 by a part 24,indicated in broken line, of incandescent body 23 which has been left inplace. A plug can also be inserted here.

In the design shown in FIGS. 14 and 15, active parts of burner channels36 are formed by individual channels 38, which run obliquely to the axisof the burner channel in incandescent body 33. In a modification of thedesign shown here, a central portion of channel 37 can also extendcompletely through incandescent body 33 to the outside surface.

FIGS. 12 and 13 and FIGS. 14 and 15 show four radial spaces 28 and fourindividual channels 38, respectively. However, a different number ofspaces or channels can be selected. Both even and odd numbers of suchradial spaces or individual channels are possible.

FIGS. 16 and 17 show a design for an incandescent body 33 that is offundamental importance regardless of the type, design, or arrangement ofthe burner channels. The burner channels or, in this case, their parts38 (corresponding approximately to a design in accordance with FIGS. 14and 15) terminate in recesses 21 external to or in the front surface ofincandescent body 33. This provides effective protection against theundesirable effects of external air currents. In the specific exampleshown here, recesses 21 form areas that are surrounded in a framelikefashion by riblike projections 22 of incandescent body 33.

FIG. 18 shows a similar design with recesses 21 in the front surface ofincandescent body 3. In this case, burner channels 6 are present whichmore or less correspond to the designs shown in FIGS. 1-4 and FIGS.6-11.

All of the individual features and combinations of features mentioned inthe above description or shown in the drawings are to be regarded aspart of the invention, excepting those which are already known from thestate of the art.

What is claimed is:
 1. A radiant burner capable of being operated with amixture of gaseous or vaporized fuel and air comprising:a hollow housinghaving inlet and outlet openings; said inlet opening receiving theair/fuel mixture; said outlet opening being spaced from said inletopening whereby the hollow space between said inlet and outlet openingsdelivers the air/fuel mixture entering through said inlet opening towardsaid outlet opening; a burner head comprised of an incandescent bodybeing positioned within said outlet opening; said incandescent bodyhaving a plurality of individual burner channels extending through saidincandescent body, said openings communicating with said hollow space;the surface of said incandescent body exposed to said hollow interiorspace being provided with metallic liming means; said metallic limingmeans providing a substantially impenetrable seal to prevent cracks orfractures which may develop in the incandescent body from having aharmful effect upon the operation of the burner; said metallic liningmeans having inlet openings each communicating with an associated one ofsaid burner channels for enabling the air/fuel mixture passing throughsaid hollow interior space to be delivered into said channels.
 2. Theradiant burner of claim 1 wherein each of said burner channels have alength L, portions of said metallic lining means defining said openingsextending at least partially into its associated channel.
 3. The radiantburner of claim 1 wherein said channels comprise an inlet end adjacentto and communicating with said hollow interior space and an outlet endterminating in a surface of said burner element remote from said hollowinterior space;each channel having at least a portion thereof whichwidens as it approaches the outlet end.
 4. The radiant burner of claim 1wherein said channels taper inwardly from the ends communicating withsaid hollow space toward an intermediate portion thereof and thereaftertaper outwardly from the intermediate portion thereof toward the outletend of each channel removed from said hollow space.
 5. The radiantburner of claim 1 wherein each channel has an inlet end adjacent saidlining, each channel terminating in an outlet end on the surface of theincandescent body external to said housing which is larger in size thanits inlet.
 6. The radiant burner of claim 5 wherein each outlet openinghas a substantially cross-shaped configuration.
 7. The radiant burner ofclaim 1 wherein each channel has an inlet end communicating with saidhollow interior space and a plurality of outlet ends communicating withsaid inlet and outlet ends and terminating on the surface of saidincandescent body external to said housing.
 8. The radiant burner ofclaim 7 wherein the outlet ends communicating with a common inlet endare arranged at equispaced intervals about an imaginary center point onthe surface of said incandescent member which point is equidistant fromthe centers of said outlet openings.
 9. The radiant burner of claim 8wherein there are four outlet openings communicating with a common inletopening.
 10. A process for producing a burner head for a radiant burnercomprising the steps of:providing an incandescent body having first andsecond opposing major surfaces and a periphery extending between saidmajor surfaces; forming a plurality of channels in said incandescentbody, which channels communicate between first and second opposing majorsurfaces; forming a metallic lining conforming to the shape of one ofthe major surfaces of said incandescent body; joining said lining andsaid incandescent body together; forming inlet openings in said metalliclining, each being coaxial with one of said channels, including formingsaid metallic lining to extend at least partially into each channel, theportion of the lining extending into each channel terminating in saidinlet opening; mounting said burner head within the open end of a hollowsupporting housing engaging the burner head about the periphery thereof;said housing and burner head defining a hollow interior space; providingat least open opening in said housing for introducing fuel and/or airwhich ultimately flows into said channels; positioning said burner headin said housing with said lining means facing said hollow interiorspace.
 11. A method for producing a burner head for a radiant burnercomprising the steps of:forming a metallic lining provided with aplurality of openings, providing a compound for forming an incandescentbody; applying said compound to one surface of said lining and allowingsaid compound to harden; providing channels in said compound eachcommunicating with an associated one of the openings in said lining. 12.The method of claim 11 wherein said channels are formed after hardening.13. The method of claim 11 wherein said channels are formed prior tohardening.
 14. The method of claim 13 wherein said compound is appliedto said lining by tamping.
 15. The method of claim 14 wherein saidcompound is applied to said lining by spraying.
 16. The method of claim11 wherein said incandescent body is joined to said lining by means ofan intermediate layer positioned upon said lining prior to applicationof said compound.
 17. The method of claim 16 wherein said intermediatelayer comprises a non-woven fabric.
 18. A radiant burner, for receivinga mixture of gaseous or vaporized fuel and air and which includes ahollow housing having inlet and outlet openings spaced apart by a hollowinterior region, and a burner head positioned in said outlet opening andincluding an incandescent body that contains individual burner channelscommunicating with said hollow interior region, the cross-sectional areaof each of said burner channels increasing in size from a first locationa predetermined distance from the surface of the incandescent bodyfacing the hollow interior region to a second location along saidchannel further removed from said first location, the surface of theincandescent body facing said hollow interior region being provided witha metal lining having inlet portions each extending partially into anassociated one of the burner channels and terminating in an openingaligned with its associated burner channel, said metal lining beingsubstantially impenetrable except for the channel inlets.
 19. A radiantburner in accordance with claim 18, wherein on the side of the metallining (7) facing away from the incandescent body (3), there is provideda barrier (14) for dividing said hollow interior space into first andsecond chambers, said first chamber receiving at least one component ofthe fuel-air mixture, and said second chamber receiving the remainingcomponent of said fuel-air mixture;each of the burner channels directlyreceiving the component introduced into said first chamber, and aplurality of supply lines directing the component introduced into saidsecond chamber to said channels.
 20. A radiant burner in accordance withclaim 18, wherein the inlet sections (8) and the remainder of the lining(7) are formed in a single member which serves as said lining.
 21. Aradiant burner in accordance with claims 18 or 20, wherein the inletsections (8) are provided in a platelike workpiece used as the lining(7), each of said inlet sections having a shape conforming to thesurface of the incandescent body facing said hollow interior region. 22.A radiant burner in accordance with claim 19, wherein one end of each ofthe supply lines (17) extends at least partially into one of the burnerchannels (6).
 23. A radiant burner in accordance with claim 22, whereinthe burner channels (6) have a circular cross-section, at least in thearea into which the supply lines (19, 20) extend; and the supply lines(19, 20) have a polygonal cross-section, at least in the portion oftheir length which extends into the burner channels (6).
 24. A radiantburner in accordance with claim 23, wherein the supply lines (17, 19,20) are supported by one of the burner channels (6) and the inletsections (8) associated with the burner channels (6).
 25. A radiantburner in accordance with claim 22, wherein the burner channels (6')have a polygonal cross-section, at least in the region into which thesupply lines (17) extend; and the supply lines (17) have a circularcross-section, at least at that portion of their length which extendsinto the burner channels (6').
 26. A radiant burner in accordance withclaim 18, wherein the inlet sections (8') are independent from thelining (7), each of said inlet sections being joined to the lining. 27.A radiant burner in accordance with claim 18, wherein the inlet sections(8) extend into said burner channels and have a length which is at leasthalf of the total length (L) of the burner channels (6).
 28. A radiantburner in accordance with claim 18, wherein an intermediate layer (10)is provided between the incandescent body (3) and the lining (7) forcompensating for any irregularities in the facing surfaces of theincandescent body and the lining.
 29. A radiant burner in accordancewith claim 18, wherein at least in a region near the surface of theincandescent body (23) remote from said hollow interior region, each ofthe burner channels (26, 36) has a substantially star-shapedcross-section comprised of a central region (27) and radial portions(28) extending outward from the central region to the exterior of theincandescent body (23).
 30. A radiant burner in accordance with claim29, wherein the central region (27) of said channels communicates withthe surface of the incandescent body (23) remote from said hollowinterior region.
 31. A radiant burner in accordance with claim 29,wherein the central region (27) of said channels is closed in the regionadjacent to the surface of the incandescent body (23) remote from saidhollow interior region.
 32. A radiant burner in accordance with claim18, wherein at least in a region near the surface of the incandescentbody (33) remote from said hollow interior region, each of the burnerchannels (26, 36) has at least two individual obliquely oriented channelportions (38).
 33. A radiant burner in accordance with claim 18, whereinthe burner channels (6, 6', 26, 36) terminate in recesses (21) in theincandescent body (3, 23, 33) said recesses being provided in thesurface of the incandescent body remote from the hollow interior region.34. A radiant burner in accordance with claim 33, wherein the recesses(21) are surrounded by integral riblike projections (22) provided in theincandescent body (3, 23, 33).
 35. A radiant burner in accordance withclaim 18, wherein the side of the lining (7) facing away from theincandescent body (3) cooperates with said housing to form the boundaryof a chamber (2) for receiving the fuel-air mixture.